The IP addresses for ns1 and ns2 should be in the glue records you set up with the registrar. Regardless if they are set up in a mast-mast or mast-slave, if the IP's are right, it should work. Now if for some reason you only have ns1 in the glue records and ns2 is ONLY resolvable from a query directly to ns1, yeah all your stuff would go down if ns1 failed. It wouldn't be worth having 2 name servers at that point.

I first heard of Dotster today actually because I had to deal with the fallout of their MX record mishap on all their domains. They really screwed a lot of people over with that but it's unrelated here I guess. So I don't know much about them but if I couldn't fully control where my name servers are and where they point to, I would switch providers. I found the link below online, so I'm not sure if you tried that already or if something changed but it's a short video of what you need essentially.